Fuel cell and analysis device that comprise it

ABSTRACT

A fuel cell comprising: at least one microfluidic channel that allows the capillary flow of at least one suitable fluid for generating electricity, at least one receiving absorbent region coupled to each microfluidic channel, at least one collecting absorbent region coupled to each microfluidic channel, a cathodic zone coupled to each microfluidic channel, and an anodic zone coupled to each microfluidic channel, where each receiving absorbent region and each collecting absorbent region are coupled to one of the microfluidic channels such that when a fluid suitable for generating electricity is deposited in the receiving absorbent region, it flows by capillary action through the microfluidic channel to reach the collecting absorbent region where it is absorbed. As well as an analysis device comprising one or more of these fuel cells.

The present invention relates to a fuel cell that can be used forsupplying power within an analysis device, preferably a lateral flowtest strip, more preferably autonomous.

STATE OF THE ART

A fuel cell is a device that converts chemical energy of a fuel intoelectrical energy, said conversion takes place as long as the fuel issupplied to the cell. These devices have been developed for more than adecade and have recently begun to find opportunities in, for example,medical applications.

Fuel cells differ from conventional batteries in that the fuel cellsallow the continuous replenishment of the consumed reagents, i.e.producing electricity from an external source of fuel and oxygen asopposed to the limited capacity of energy storage which has a battery.In addition, the electrodes in a battery react and change according tohow it is loaded or unloaded, whereas in a fuel cell electrodes arecatalytic and relatively stable. Moreover, conventional batteriesconsume solid reactants, and once depleted, must be discarded orrecharged with electricity. Generally, in a fuel cell the reagent(s)flow inwardly and the reaction products flow outwardly. This flow ofreactant(s) is normally achieved by using, for example, external pumps,which may result in a complex and expensive configuration of the fuelcell.

For instance, U.S. 2009092882 A1 (Kjeang E. et al.) discloses amicrofluidic fuel cell architecture with flow through the electrodes.The anode and cathode electrodes are porous and comprise a network ofinterstitial pores. A virtual insulator is located between theelectrodes, in an electrolyte channel. The virtual insulator consists ofa co-laminar flow of an electrolyte. An inlet directs substantially allthe flow of the liquid reactant through the porous electrode. Thisconfiguration has the disadvantage of requiring means, e.g. an externalpump, to provide the liquid reagent through the inlet for the fuel cellto operate.

Very recently, it has been disclosed that the integration of a microdirect methanol fuel cell can provide both pumping and electrical powerto a microfluidics platform successfully [J P Esquivel, et al., Fuelcell powered microfluidic platform for lab on a chip applications, Labon a Chip (2011) DOI: 10.1039/C1LC20426B]. The electrochemical reactionsthat take place in the fuel cell produce CO₂, which is normallyconsidered a residue without any utility. In this case, however, the CO₂is accumulated and used for pumping a fluid into the microfluidicplatform. Therefore, the pumping of a fluid, which may be a reagent of afuel cell, is achieved without need for an external pump, but it isnecessary to use a methanol fuel cell for this purpose. Thus, in thiscase, also the obtained configuration is complex and expensive. Also,using a first fuel cell to cause a flow of a reagent of a second fuelcell would result in a complex system.

Furthermore, fuel cells known to date may contain significant amounts ofnon-biodegradable materials, so that these fuel cells eventuallyresulting in non-biodegradable wastes, not environmentally friendly.

DETAILED DESCRIPTION OF THE INVENTION

In a first aspect, the present invention provides a fuel cell comprisingat least one microfluidic channel that allows the capillary flow of atleast one suitable fluid for generating electricity, at least onereceiving absorbent region, at least one collecting absorbent region,one cathodic zone comprising at least one cathode and one anodic zonecomprising at least one anode. Each receiving absorbent region, where atleast one fluid can be deposited, is coupled to one of the microfluidicchannels such that the microfluidic channel can receive from thereceiving absorbent region the said fluid or fluids by capillary action.Each collecting absorbent region is coupled to one of the microfluidicchannels so that it can receive from that microfluidic channel bycapillary the fluid or fluids previously deposited in the receivingabsorbent regions coupled to the same microfluidic channel. Afterreceiving this fluid or fluids in the collecting absorbent region, theseare absorbed in said region allowing the continuation of the flow bycapillary action once the microfluidic channel has become saturated. Atleast one cathode and at least one anode are coupled to eachmicrofluidic channel so that electrical energy can be generated while atleast one suitable fluid for generating electricity flows through themicrofluidic channel.

In the present invention the term “suitable fluid to generateelectricity” is understood as any fluid comprising at least oneoxidizing or reducing substance, so that this fluid can interact withone of the cathodes or anodes to generate electricity. Preferably thefluid is a liquid, although it may contain suspended particles.

In addition to the appropriate flow to generate electricity, the fuelcell of the present invention can also incorporate at least oneelectrolytic fluid in one of the receiving regions coupled to at leastone microfluidic channel. Preferably, this electrolytic fluid is placedin a receiving region different from the one(s) used to deposit any ofthe suitable fluids to generate electricity.

The fuel cell of the present invention has the advantage that the flowof suitable fluids for generating electricity, i.e. the flow ofreactants is achieved by capillary action, eliminating the need of, forexample, pumps or other means to flow these reactants. In this regard,one of the key points of the fuel cell described in this patentapplication is that absorption by the collecting absorbent region causesthe continuation of the flow by capillary action once the microfluidicchannel has become saturated. The fuel cell of the present invention isvery simple and can be very cheap, since the microfluidic channel andthe absorbent regions may be manufactured from materials that areabundant, cheap and biodegradable such as, for example, paper-basedmaterials.

Each of the microfluidic channels mainly comprises a wicking materialwith adequate porosity to allow the flow of at least one fluid capableof generating electricity, this fluid being initially deposited on oneof the receiving absorbent regions. Preferably, each of the microfluidicchannels within the fuel cell may majorly comprise a material selectedindependently from the group consisting of hydrophilic polymer, textilefiber, glass fiber, cellulose and nitrocellulose; being especiallypreferred that such material is biodegradable.

In some even more preferred embodiments, the fuel cell of the presentinvention comprises at least one microfluidic channel can be made ofpaper, such as, for example, filter paper, tissue paper, cellulose paperor writing paper. As mentioned before, this type of material contributessignificantly to make the fuel cell biodegradable.

In other preferred embodiments, the present invention relates to thefuel cell that may comprise at least one receiving absorbent region andat least one collecting absorbent region as described in this patentapplication, where each of the receiving and collecting absorbentregions, independently, may comprise a material selected from the groupconsisting of hydrophilic polymer, textile fiber, glass fiber, celluloseand nitrocellulose; being especially preferable that such material isbiodegradable.

Preferably, the fuel cell of the present invention may comprise at leastone microfluidic channel, and each microfluidic channel may comprise atleast one receiving absorbent region and at least one collectingabsorbent region as described in this patent application, where themicrofluidic channels and the receiving and collecting zones coupled toeach of them may comprise a material selected independently from thegroup consisting of hydrophilic polymer, textile fiber, glass fiber,cellulose and nitrocellulose; being especially preferred that allmicrofluidic channels and receiving and collecting areas coupled to themmostly comprise biodegradable materials.

In other even more preferred embodiments, the fuel cell of the presentinvention comprises at least one receiving absorbent region, at leastone collecting absorbent region and all of them can be made of paper,such as, for example, filter paper, tissue paper, cellulose paper orwriting paper. Again, this type of material for absorbent regions alsocontributes significantly to make the fuel cell very biodegradable.

In either embodiment of the present invention, any cathode and any anodecoupled to each of the microfluidic channels may comprise a materialmainly selected from the group consisting of noble metal, non-noblemetal, enzymes and bacteria. In case that any one of the electrodescomprises enzymes or bacteria, the pH of the medium can be acidic, basicor neutral depending upon the stability of these enzymes or bacteria atdifferent pH. Preferably, the pH of the medium is one in which themetals, enzymes or bacteria present in any one of the electrodes have ahigher stability and catalytic activity. To obtain this optimum pH ispossible to immobilize suitable substances within the fuel cell.

In other preferred embodiments, the present invention relates to a fuelcell as described in this patent application, where at least one of theelectrodes coupled to each microfluidic channel, either the cathode orthe anode, may comprise at least one enzymatic catalyst. In a morepreferred embodiment, each microfluidic channel comprises an anode and acathode, and only one of these two comprises an enzymatic catalyst.Preferably, the enzyme catalyst may be selected from the groupconsisting of glucose oxidase, glucose dehydrogenase, aldehydedehydrogenase, fructose dehydrogenase, laccase, urease andmicroperoxidase. This feature also contributes significantly to make thefuel cell of the present invention biodegradable, since the enzymes arebiological molecules.

In other preferred embodiments, the present invention also relates to afuel cell as described in this patent application, wherein eachmicrofluidic channel has coupled a cathodic zone comprising at least onecathode and this may have a porous structure to receive and interactwith oxygen from the atmosphere. This feature can help to obtain a moreefficient oxidation of the fuel substance(s) and therefore an improvedefficiency of the fuel cell.

As mentioned above, the fuel cell of the present invention may comprisemore than one microfluidic channel, thereby generating a larger amountof energy. Additionally, the fuel cell of the present invention maycomprise a single microfluidic channel, which leads to a device withgreater simplicity.

The fuel cell of the present invention may comprise more than onereceiving absorbent region coupled to each microfluidic channel, inwhich case the different receiving absorbent regions can be totallyindependent or they may be separated regions and located on the samephysical support, also called sub-regions in this patent application.

In other preferred embodiments, the receiving and collecting absorbentregions can be located at different heights, which facilitates the flowby capillary action through the microfluidic channel.

Additionally, in other preferred embodiments of the present invention,at least one of the receiving absorbent regions may comprise at leastone solid substance selected from the group consisting of oxidizing,reducing and electrolyte. This (these) substance(s) are solubilized whenthey are in contact with a liquid, preferably aqueous, leading to themovement of this fluid by capillarity through the microfluidic channel.

In other preferred embodiments, the fuel cell of the present inventionmay comprise a single microfluidic channel that allows the capillaryflow of at least one suitable fluid for generating electricity.

In other preferred embodiments, the fuel cell of the present inventionmay comprise a maximum of three receiving absorbent regions separatedfrom each other, each coupled to the microfluidic channel. Preferably,the fuel cell comprises a single microfluidic channel.

In even more preferred embodiments, the fuel cell of the presentinvention may comprise two receiving absorbent regions separated fromeach other, preferably located in the same physical support, where inthe receiving absorbent region closest to the cathode can be placed oneor more catholyte fluids, so that the cathode(s) can fully interact withthe fluid when it flow through the microfluidic channel by capillaryaction. Analogously, in the receiving absorbent region closest to theanode zone may be deposited one or more anolyte fluids, so that theanode(s) can fully interact with the anolyte fluid when flowing throughthe channel microfluidic by capillary action. An especially preferredembodiment of this embodiment is described below (see FIG. 1 b).

The catholyte fluid may comprise one or more oxidant substances,preferably the oxidant substances can be selected from the groupconsisting of hydrogen peroxide and diluted oxygen.

Furthermore, the anolyte fluid may include one or more substancesselected from the group consisting of methanol, ethanol, formic acid,glucose, glycerol and urea.

The embodiments of the previous paragraph allow obtaining energy in amore efficient way, since they may permit a “clean” oxidizing processand a “clean” reduction process substantially isolated from each other.

In other still more preferred embodiments, the fuel cell of the presentinvention comprises a third receiving absorbent region, between the twomentioned above, and separated from the other two receiving absorbentsregions, preferably all located on the same support, where in this thirdreceiving absorbent region can be deposited at least one electrolytefluid, so that this electrolyte fluid can at least partially maintainseparated the catholyte and anolyte fluids when flowing through themicrofluidic channel by capillary action. An especially preferredembodiment is described below (see FIG. 1 c).

The electrolyte fluid may comprise one or more substances selected fromthe group consisting of sulfuric acid, sodium sulfate, phosphatebuffered saline, potassium hydroxide and sodium hydroxide.

The embodiments of the previous paragraphs enable the production ofenergy even more efficiently, since the flow of the electrolyte fluidmay delay the mixing of catholyte and anolyte fluids, obtaining afurther isolation of oxidation and reduction processes that lead toelectrical energy in the fuel cell of the invention.

In a second aspect, the present invention provides an analysis devicecomprising:

i) at least one fuel cell such as described in this patent application,ii) at least one analysis microfluidic channel that allows the capillaryflow of a liquid sample,iii) at least one receiving absorbent region coupled to each analysismicrofluidic channel, andiv) at least one collecting absorbent region coupled to each analysismicrofluidic channel,where each receiving absorbent region and each collecting absorbentregion are connected to an analysis microfluidic channel so that whenthe liquid sample is deposited in the receiving absorbent region, itflows by capillary action through the analysis microfluidic channel toreach the collecting absorbent region where it is absorbed.

Preferably, the analysis device as described in the present inventionmay be an analysis test strip, more preferably may be a test strip knownas “lateral flow test strip”.

In preferred embodiments, the present invention provides an analysisdevice, preferably a test strip, as described in this patent applicationthat may comprise at least one conductive track connecting any one ofthe fuel cells within the test device with at least one element selectedfrom the group consisting of at least one electrochemical sensor, atleast one display system to visualize the results of the analysis and atleast one electronic circuit.

Preferably, when the analysis device is connected to more than one ofthe foregoing, these can also be linked together by conductive tracks.

The additional features mentioned in the preceding paragraphs may beexternal to the test device, in which case to use the analysis device ofthe present invention, it will connect to at least one electrochemicalsensor, to at least one display system and to at least one electroniccircuit.

In other preferred embodiments, the analysis device, which preferably isthe test strip as described in this patent application may furthercomprise at least one electrochemical sensor coupled to each analysismicrofluidic channel, so that each of these sensors can interact incombination with appropriate electrical input signals, with the liquidsample as it flows by capillary action through the analysis microfluidicchannel, and such interaction produces electrical output signalsrepresenting the result of the test. The test device can also compriseat least one conductive track connecting at least one of theelectrochemical sensors coupled to each analysis microfluidic channelwith at least one fuel cell. According to these preferred embodiments,the analysis device can be used without connecting it to externalelectrochemical sensors.

In further preferred embodiments, the analysis device of the presentinvention may comprise at least one display system to visualize theresults and at least one conductive track connecting at least one of thedisplay systems with at least one fuel cell comprised in the analysisdevice. Preferably, the analysis device also comprises at least oneelectrochemical sensor coupled to each analysis microfluidic channel,and at least one conductive track connecting at least one of theseelectrochemical sensors with at least one of the fuel cells within theanalysis device. Additionally, the analysis device of the presentinvention may also comprise at least one conductive track connecting atleast one of the display systems with at least one of theelectrochemical sensors comprised within the device.

In further preferred embodiments, the analysis device of the presentinvention may comprise at least one electronic circuit and at least oneconductive track connecting at least one of the electronic circuits withat least one of the fuel cells comprised within the analysis device.Preferably, the analysis device also comprises at least oneelectrochemical sensor coupled to each analysis microfluidic channel andat least one conductive track connecting at least one of theseelectrochemical sensors with at least one of the fuel cells included inthe analysis device. Additionally, the analysis device of the presentinvention may also comprise at least one conductive track connecting atleast one of the electronic circuits with at least one of theelectrochemical sensors comprised within the device.

In other preferred embodiments, the analysis device as described in thispatent application may comprise:

i) at least one fuel cell as the described in this patent application,ii) at least one analysis microfluidic channel that allows the capillaryflow of a liquid sample,iii) at least one receiving absorbent region coupled to each analysismicrofluidic channel,iv) at least one collecting absorbent region coupled to each analysismicrofluidic channel,v) at least one electrochemical sensor connected to each analysismicrofluidic channel,vi) at least one display system to visualize the results of theanalysis,vii) at least one electronic circuit, andviii) a plurality of conductive tracks connecting each one of them atleast two of the elements included in the analysis device and selectedfrom the group consisting of at least one of the electronic circuits, atleast one of the fuel cells, at least one of the electrochemical sensorsand at least one of the display systems to visualize the results.

The network of conductive tracks may be such that the electronic circuitcan receive electricity from one of the fuel cells, provide each of theelectrochemical sensors suitable electrical input signals, obtainelectrical signals output from each of the electrochemical sensors, andprovide one of the display systems with the electrical output signalsrepresenting the results of the analysis.

The present invention provides an analysis device, preferably a lateralflow test strip, where the flow of appropriate fluid to generateelectricity and the liquid sample to be tested can be achieved bycapillary without external means, such as for example specific pumps orsimilar means which can result in complex and expensive configurations.Furthermore, this analysis device may be completely autonomous orindependent through the integration of at least one fuel cell asdescribed in this patent application with other suitable means, such aselectrochemical sensors, electronic circuits and display systems, whichcan be powered with the energy from the fuel cell.

In some preferred embodiments, the analysis device of the presentinvention comprises only one analysis microfluidic channel.

In other preferred embodiments, the test strip as described in thispatent application may comprise:

i) a fuel cell such as described in this patent application,ii) an analysis microfluidic channel that allows the capillary flow of aliquid sample,iii) a maximum of three receiving absorbent regions coupled to theanalysis microfluidic channel,iv) a collecting absorbent region coupled to the analysis microfluidicchannel,v) an electrochemical sensor connected to the analysis microfluidicchannel,vi) a display system to visualize the results of the analysis,vii) an electronic circuit, andviii) a plurality of conductive tracks connecting each one of them atleast two of the elements included in the test strip and selected fromthe group consisting of the electronic circuit, the fuel cell, theelectrochemical sensor and the system to display results.

In other preferred embodiments of the present invention, the receivingand collecting absorbent regions coupled to each analysis microfluidicchannel are made of paper, this feature contributes to thebiodegradability of the analysis device of the present invention.

In other preferred embodiments, the receiving absorbent regions coupledto each analysis microfluidic channel can be comprised, independently,in one of the receiving absorbent regions comprised in one of the fuelcells.

In other preferred embodiments, the collecting absorbent regions coupledto each analysis microfluidic channel can be comprised, independently,in one of the collecting absorbent regions comprised in one of the fuelcells. Preferably, each of the receiving absorbent regions coupled toeach analysis microfluidic channel can be comprised, independently, inone of the receiving absorbent regions comprised in the same fuel cell.

In even more preferred embodiments, the analysis device as described inthis patent application may comprise a single fuel cell, a singleanalysis microfluidic channel, at least one receiving absorbent regioncoupled to the analysis microfluidic channel and a collecting absorbentregion coupled to the analysis microfluidic channel, where the differentreceiving absorbent regions may be comprised, independently, in any oneof the receiving absorbent regions comprised in the fuel cell.

These preferred embodiments allow simultaneously depositing the liquidsample, preferably biological sample, in a receiving absorbent regioncoupled to a microfluidic channel comprised in the fuel cell and in areceiving absorbent region coupled to the analysis microfluidic channel.In this way, the same sample to analyze can also act as fuel or reagentto produce electrical energy.

Each of the analysis microfluidic channels mainly comprises a wickingmaterial with adequate porosity to allow the flow of liquid sampleinitially deposited on one of the receiving absorbent regions.Preferably, the test strip of the present invention comprises at leastone analysis microfluidic channel which in turn comprises a materialselected from the group consisting of hydrophilic polymer, glass fiber,cellulose and nitrocellulose.

In some even more preferred embodiments, the analysis device of thepresent invention comprises at least one analysis microfluidic channelthat can be made of paper. As mentioned before, this type of materialcontributes significantly to make the analysis device biodegradable,especially when the elements of the fuel cell are also made of paper.

In other embodiments of the invention, each electrochemical sensor ofthe analysis device may be based on carbon electrodes. This type ofmaterial for the electrochemical sensors also contributes significantlyto make the analysis device of the invention more biodegradable.

In other embodiments of the invention, the electronic circuit ofanalysis device may be a silicon-based microelectronic circuit.Additionally, the display system may be a screen, more preferably ascreen printed on paper.

In other embodiments of the invention, at least one of the conductivetracks of the analysis device may be made of carbon. This type ofmaterial for the conductive tracks can make the analysis device highlybiodegradable.

A very important advantage of some of the embodiments described in thispatent application is that a fuel cell and a test strip comprising afuel cell as described in this patent application, may have very smalldimensions. This is possible thanks to the simple structure that thefuel cell and the test strip may have, on the type of materials that canbe used to produce such a simple configuration. Another advantage isthat both the fuel cell as the preferred test strip described in thispatent application can have a very high level of biodegradability.

BRIEF DESCRIPTION OF THE FIGURES

Preferred embodiments of the present invention are described in thefollowing nonlimiting examples, with reference to the accompanyingfigures, in which:

FIG. 1 a: Schematic representation of a top view of a fuel cellaccording to a first preferred embodiment of the invention.

FIG. 1 b: Schematic representation of a top view of a fuel cellaccording to a second preferred embodiment of the invention.

FIG. 1 c: Schematic representation of a top view of a fuel cellaccording to a third preferred embodiment of the invention.

FIG. 1 d: Schematic representation of a 3D paper sheet having amicrofluidic channel in accordance with preferred embodiments of theinvention.

FIG. 2 a: Schematic representation of a top view of a lateral flow teststrip according to preferred embodiments of the invention.

FIG. 2 b: Schematic representation of a top view of a lateral flow teststrip in accordance with other preferred embodiments of the invention.

FIG. 2 c: Schematic representation of a top view of a lateral flow teststrip in accordance with other preferred embodiments of the invention.

FIG. 3 a: Schematic representation of catholyte and anolyte fluidsflowing through a microfluidic channel as shown in FIG. 1 b.

FIG. 3 b: Schematic representation of a 3D configuration of amicrofluidic channel and coupled cathodic and anodic zones, throughwhich catholyte and anolyte fluids flow in accordance with preferredembodiments of the invention.

FIG. 3 c: Schematic representation of catholyte, anolyte and electrolytefluids flowing through a microfluidic channel as shown in FIG. 1 c.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 1 a shows a schematic representation of a top view of a fuel cellaccording to a first particularly preferred embodiment of the invention.This fuel cell comprising a microfluidic channel (10), a receivingabsorbent region (11) coupled to the microfluidic channel (10) at oneend of said microfluidic channel (10), and a collecting absorbent region(12) coupled to the microfluidic channel (10) at the opposite end ofsaid channel. In order to facilitate capillary action through themicrofluidic channel, it is preferred that the end which is coupled tothe collecting absorbent region (12) and the end to which is coupled thereceiving absorbent region (11) are located at different heights, remainindifferent which end is higher.

This particularly preferred configuration of the fuel cell of thepresent invention allows to deposit in the receiving absorbent region(11) at least one suitable fluid for electricity generation, i.e. afluid comprising fuel reactants. As well as allowing the flow of thesefluids by capillary action through the microfluidic channel (10), untilreaching the collecting absorbent region (12) where fluids are absorbed,thereby allowing the continued flow through the microfluidic channel(10).

The fuel cell of FIG. 1 a also comprises a cathodic zone comprising atleast one cathode (13) and an anodic zone comprising at least one anode(14) coupled to the microfluidic channel (10) so that the cathodic zone(13) and the anodic zone (14) can generate electrochemical energy due toits interaction with at least one fluid comprising fuel reactants whenthese flow continuously through the microfluidic channel (10) bycapillary action. In this embodiment, the fluid deposited in the singlereceiving absorbent region may comprise reducing and oxidizing species,such that the interaction of the cathodic zone (13) with the reducingspecies and interaction of the anodic zone (14) with the oxidizingspecies may lead to an electrochemical voltage between the cathodic zone(13) and the anodic zone (14). In this particular embodiment, thecathodic zone (13) is placed on a lateral side of the microfluidicchannel (10), and the anodic zone (14) is placed on the opposite side ofthe microfluidic channel (10).

Still referring to FIG. 1 a, the receiving absorbent region (11) maycomprise at least one chemical substance which has been previouslyimmobilized in a defined area of the receiving absorbent region (11), sothat the substance can be solubilized by adding an external liquid,preferably an aqueous liquid.

FIG. 1 b is a schematic representation of a top view of a fuel cellaccording to a particularly preferred second embodiment of theinvention. This configuration is very similar to the configuration ofFIG. 1 a with the difference that the receiving absorbent region (11)comprises two receiving absorbent sub-regions, identified as (11 a) and(11 b) which are separated from each and located in the same physicalsupport. In the first receiving absorbent sub-region (11 a) candeposited a catholyte fluid, giving rise to reduced species to interactwith the cathodic zone (13), and in the second receiving absorbentsub-region (11 b) can be deposited anolyte fluid comprising oxidizingspecies that can interact with the anodic zone (14). Alternatively, thefirst receiving absorbent sub-region (11 a) may comprise an oxidizingsubstance previously immobilized in an area of the first receivingabsorbent sub-region (11 a) and the second receiving absorbentsub-region (11 b) may comprise a reductive substance previouslyimmobilized in an area of the second receiving absorbent sub-region (11b). Then, immobilized oxidizing and reducing substances can besolubilized for example by the addition of an external liquid,preferably an aqueous liquid.

In the embodiment of FIG. 1 b, the microfluidic channel (10) comprisestwo branches (18), so that the receiving absorbent sub-region (11 a) iscoupled to the microfluidic channel (10) through one of these branches(18) and the second receiving absorbent sub-region (11 b) is coupled tothe microfluidic channel (10) through a second of said branches (18).Said first branch and the cathodic zone (13) are arranged substantiallyon the same side of the microfluidic channel (10), so that the cathodiczone (13) can substantially interact completely with the catholyte fluidwhen it flows through the microfluidic channel (10). Equivalently, thesecond branch and the anodic zone (14) are arranged substantially on thesame side of the microfluidic channel (10), so that the anodic zone (14)can substantially interact completely with anolyte fluid when it flowsthrough the microfluidic channel (10). More details about the flows ofthe catholyte and anolyte fluids are described later.

The configuration described in the previous paragraph implies a relativepositioning between the first receiving absorbent sub-region (11 a) andthe cathodic zone (13), and between the second receiving absorbentsub-region (11 b) and the anodic zone (14), which allows the productionof electrochemical energy more efficiently than in the embodiment ofFIG. 1 a. In fact, with this preferred configuration of the fuel cell ofthe present invention can be obtained a “clean” interaction between thecatholyte fluid comprising at least one reducing species and thecathodic zone (13), and a “clean” interaction between the anolyte fluidcomprising at least one oxidizing species and the anodic zone (14), andconsequently the fuel cell is more efficient.

In this regard, FIG. 3 a shows the configuration of a microfluidicchannel (10), a cathodic zone (13) and an anodic zone (14) similar tothe one comprised in the fuel cell shown in FIG. 1 b. FIG. 3 a alsoshows how a catholyte fluid (31) and an anolyte fluid (30) can flowthrough the microfluidic channel (10). Particularly, the catholyte fluid(31), which comprises reducing species, can flow so that it can achievea substantially complete interaction between this and the cathode(s)contained in the cathodic zone (13). Equivalently, the anolyte fluid(30), which comprises oxidizing species can flow so that it can achievea substantially complete interaction between this and the anode(s)contained in the anodic zone (14).

FIG. 3 a also shows how, in this particularly preferred embodiment, thecatholyte fluid (31) and the anolyte fluid (30) can start to mix afteradvancing a certain distance, forming an area called diffusion zone(32). In this especially preferred embodiment of the invention, thecathodic zone (13) and the anodic zone (14) are positioned in themicrofluidic channel (10) at a distance sufficiently short with respectto the end where the receiving absorbent sub-regions (11 a) and (11 b)are coupled to prevent that the diffusion zone (32) comes into contactwith any one of the cathodes comprised in the cathodic zone (13), withany one of the anodes comprised in the anodic zone (14), or both. Thus,although the catholyte fluid (31) and the anolyte fluid (30) can befinally mixed, in this particularly preferred embodiment it is ensuredan interaction between the fluid completely catholyte (31) and thecathodic zone (13), and between the fluid completely anolyte (30) andthe anodic zone (14).

FIG. 3 b is a schematic representation of a 3D microfluidic channel (10)and the configuration of the cathodic zone (13) and the anodic zone (14)in accordance with another particularly preferred embodiment of theinvention. This configuration is an alternative to the configurationshown in FIGS. 1 b and 3 a. In this case, the first and second receivingabsorbent sub-regions (11 a), (11 b), not shown in FIG. 3 b, arearranged so that the flow of catholyte fluid (31) is achievedsubstantially above the flow of anolyte fluid (30). Accordingly, thecathodic zone (13) is disposed in an upper region of the microfluidicchannel (10) and the anodic zone (14) is disposed in a lower region ofthe microfluidic channel (10). This configuration of FIG. 3 b allows thegeneration of electrochemical energy substantially equal to theconfiguration of FIGS. 1 b and 3 a.

FIG. 1 c is a schematic representation of a top view of a fuel cellaccording to another especially preferred embodiment of the invention.In this case, the difference from the fuel cell shown in FIG. 1 b isthat this especially preferred embodiment further comprises a thirdreceiving absorbent sub-region (11 c) separated from the first andsecond receiving absorbent sub-regions (11 a) and (11 b). In this thirdabsorbent sub-region (11 c) can be deposited an electrolyte fluid, andmay be disposed in relation to the first and second absorbentsub-regions (11 a) and (11 b) so that the electrolyte fluid maintains atleast partially, the catholyte fluid (31) and the anolyte fluid (30)separate as they flow through the microfluidic channel (10) bycapillarity.

In especially preferred embodiment of FIG. 1 c, the mixture catholytefluid (31) and the anolyte fluid (30) can be delayed with respect to themixture which is produced in the configurations of FIGS. 1 b, 3 a and 3b. In this regard, FIG. 3 c shows how in this especially preferableembodiment, an electrolyte fluid (33) flowing between the catholytefluid (31) and the anolyte fluid (30) to delay the mixing of thecatholyte fluid (31) and the anolyte fluid (30). The area (34) refers tothe mixture of catholyte fluid (31) with the electrolyte fluid (33). Thearea (35) refers to the mixture of anolyte fluid (30) with theelectrolyte fluid (33). It is clearly seen that with the “intermediate”flow of electrolyte fluid (33), the diffusion zone (32) which representsthe mixture of catholyte (31) and anolyte (30) fluids which appearslater than in the embodiments without such “intermediate” flow of fluidelectrolyte (33).

In any of the above described embodiments, the microfluidic channel (10)as well as any of the absorbent regions (11) and (12), can be made of apaper based material, such as for example filter paper, paper silk,cellulose paper, writing paper, etc. Alternatively, they may be made ofother suitable materials such as e.g. nitrocellulose acetate, textiles,polymeric layers, etc. Paper-based materials suppose a low cost, so themicrofluidic channel (10) and receiving and collecting absorbentregions, (11) and (12) respectively, are preferably made of such type ofmaterial. In addition, paper is a completely biodegradable material.Therefore, paper contributes to obtaining a cheap and biodegradable fuelcell.

Furthermore, the microfluidic channel (10), as well as any of thereceiving or collecting regions comprising paper as a main material, canbe obtained by two different methods, or a combination thereof. Thefirst method involves cutting the paper into the desired shape so thatthe resulting structure corresponds to the microfluidic channel. Thecutting can be performed by mechanical action, for example, usingscissors, knives or automatic equipment such as a plotter cutter, orusing a laser, etc. The second method involves defining hydrophobicareas within the total surface of the porous material, preferably paper.The definition of hydrophobic areas can be accomplished by impregnatingthe porous matrix with photoresist, wax, teflon, hydrophobic chemicals,etc., or applying a chemical treatment to modify the wetting properties.

FIG. 1 d is a schematic representation of a 3D paper sheet having amicrofluidic channel suitable for the embodiments of the invention. Themicrofluidic channel has been achieved by defining hydrophobic areas(16) that define, in turn, a hydrophilic zone (paper) (17) whichconstitutes the desired microfluidic channel. The hydrophobic areas (16)can be obtained for example by applying any of the techniques discussedabove.

Preferably, cutting is applied to obtain the microfluidic channel (10)and receiving and collecting absorbent regions, (11) and (12)respectively, because cutting a priori is cheaper than other types ofmethods, such as for example the techniques discussed above based on thedefinition of hydrophobic areas.

FIG. 2 a is a schematic representation of a top view of a lateral flowtest strip according to especially preferred embodiments of theinvention. This test strip comprising the fuel cell described above andschematized in FIG. 1 a. This test strip also comprises an analysismicrofluidic channel (20) connected to the receiving absorbent region(11) at one end of the channel (20), and the collecting absorbent region(12) at the opposite end of channel (20). Thus, in this especiallypreferred embodiment of the present invention, the receiving absorbentregion of the analysis microfluidic channel (20) is the same as thereceiving absorbent region of the fuel cell, and the collectingabsorbent region of the analysis microfluidic channel is the same as thecollecting absorbent region of the fuel cell. The features described inrelation to FIG. 1 a with respect to the receiving absorbent region (11)and to the microfluidic channel (10) are also applicable to thispreferred embodiment of the test strip of the invention. Therefore, thisespecially preferred configuration can also allow a continuous flow offluid from the receiving absorbent region (11) to the collectingabsorbent region (12), where the fluid is absorbed allowing thecontinuation of the flow by capillarity when the analysis microfluidicchannel (20) is saturated.

Alternatively to the especially preferred embodiment described above,the test strip of the present invention may comprise a receivingabsorbent region and a collecting absorbent region, connected toopposite ends of the analysis microfluidic channel (20), being theseabsorbent regions separated from receiving (11) and collecting (12)absorbent regions coupled to the microfluidic channel (10) which formpart of the fuel cell comprised in the test strip of the invention.

In an especially preferred embodiment of the present invention as shownin FIG. 2 a, the test strip of the present invention comprises adetection zone (21) having at least one electrochemical sensor coupledto the analysis microfluidic channel (20), so that the electrochemicalsensor may interact with the sample to be tested, preferably abiological sample, when it flows by capillary through analysismicrofluidic channel (20). Such interaction, in combination withappropriate electrical input signals, can produce correspondingelectrical output signals representing the results of the test.Electrochemical sensors can be based on carbon electrodes, said materialcontributes to the biodegradability of the test strip.

This test strip can also comprise an electronic circuit (23), a displaysystem (24), preferably a screen, and a plurality of conductive tracks(22), (25) and (26) that connect the electronic circuit (23) with theanodic zone (14) and the cathodic zone (13) of the fuel cell, with thedetection zone (21), and with the display system (24). The electroniccircuit (23) may be a silicon-based microelectronic circuit.Additionally, the display system (24) can be a screen printed in paper,for example, based on suitable polymers. Additionally, the conductivetracks (22), (25) and (26) may be made of carbon. These features canmake the test strip highly biodegradable. As an alternative to carbon,the conductive tracks (22), (25) and (26) may be made of conductivepolymers, copper, gold or any combination thereof.

Conductive tracks (22) that connect the electronic circuit (23) with theanodic zone (14) and the cathodic zone (13) of the fuel cell allow theelectronic circuit (23) to receive electricity from the fuel cell.Conductive tracks (25) that connect the electronic circuit (23) withelectrochemical sensors included in the detection zone (21) allow theelectronic circuit (23) to provide adequate electrical input signals tothe electrochemical sensors (21). The electronic circuit (23) can getthese electrical input signals, necessary for electrochemical sensors(21) to properly interact with the sample to analyze, from theelectricity produced by the fuel cell according to an implemented logic.This interaction of electrochemical sensors (21) with the sample,preferably biologic, and the appropriate electrical input signals canproduce electrical output signals representing the results of theanalysis. Sensors within the detection zone (21) can send theseelectrical output signals to the electronic circuit (23) through thecorresponding conductive tracks (25). The electronic circuit (23) canconvert, according to an implemented logic, these electrical outputsignals into electrical signals that can be visualized and sends them tothe display system (24) through the corresponding conductive track (26).

The test strip of the present invention may further comprise apre-treatment region, not shown in FIG. 2 a, which can be coupled to themicrofluidic channel of the fuel cell (10) at a point between thereceiving absorbent region (11) and the cathodic (13) or anodic (14)zones. Additionally, this pre-treatment region may also be incorporatedinto the microfluidic channel analysis (20), at a point between thereceiving absorbent region of the sample (11) and the detection zone(21). This pre-treatment region may have a configuration suitable forcarrying out different types of pretreatments such as filtering,separation, screening of the liquid(s) that may flow through themicrofluidic channel of the fuel cell (10) and/or analysis microfluidicchannel (20). To design and/or build this region known principles ofpre-treatment can be used, such as those described in patentapplications WO 2009121041 A2 (A. Siegel et al) and WO 2011087813 A2 (P.Yager et al).

FIG. 2 b is a schematic representation of a top view of a lateral flowtest strip in accordance with other particularly preferred embodimentsof the invention. This test strip is very similar to the strip shown inFIG. 2 a, with the difference that the strip of FIG. 2 b includes a fuelcell of the type described with reference to FIG. 1 b, while the stripFIG. 2 a comprises a fuel cell of the type shown in FIG. 1 a.

FIG. 2 c is a schematic representation of a top view of a lateral flowtest strip in accordance with other particularly preferred embodimentsof the invention. This test strip is very similar to the strip shown inFIG. 2 b, with the only difference that the strip of FIG. 2 c comprisesa fuel cell of the type described with reference to FIG. 1 c, while thestrip FIG. 2 b comprises a fuel cell of the type shown in FIG. 1 b.

An important aspect of the strips illustrated in FIGS. 2 a, 2 b and 2 cis that the same fluid can be used as a suitable fluid to generateelectricity by the fuel cell, and as the sample to analyze in thedetection zone (21). This fluid can be a biological sample, such as, forexample, urine, blood, blood plasma, saliva, semen, sweat, etc. In thisway, this strip may be a completely stand-alone test strip, andtherefore, operate without connection to external electrochemicalsensor, display system or electronic circuit.

In some embodiments of the test strip described in this patentapplication, the detection zone (21) has the function of measuring ordetecting specific compounds in the sample, preferably biologically, toanalyze. Detection can be based on different techniques such aselectrochemical, optical, etc. Additional stages of pre-treating thesample, and the regions needed for these steps to take place in thestrip can be included before the sample reaches the detection zone (21).

An electrochemical sensor can be manufactured for example by depositionof one or more electrodes, which may be made of carbon in a porousmatrix, which may be made of paper based materials. One of theseelectrodes can be defined as a reference electrode, at least one ofthese electrodes as a counter electrode, and at least one more of theseelectrodes as a working electrode. Electrode deposition may beaccomplished by various techniques such as sputtering, evaporation,spray coating or printing techniques such as ink jet, gravure, offset,flexographic or screen printing. The electrodes can be functionalized toenhance detection capabilities. The functionalization of the electrodesmay be formed by deposition of an active material, chemical treatment,etc.

For designing and constructing the detection zone (21) can be usedsuitable known principles known to one skilled in the art, for example,those disclosed in Patterned paper substrates and as alternativematerials for low-cost microfluidic diagnostics, David R. Ballerini, XuLi and Shen Wei. Microfluidics and Nanofluidics. 2012, DOI:10.1007/s10404-012-0999-2.

The electronic circuit (23) may correspond to an electronic circuit thatcan perform various tasks related to the test results to be produced.The circuit may comprise a combination of discrete electronic componentsand/or integrated circuits. Some embodiments may use, for example, afull custom application specific integrated circuit (ASIC) forperformance improvement and reduction of area.

The circuit may comprise several blocks such as power management,instrumentation, communications, data logging, etc. The power managementblock may take the energy produced by the fuel cell and increase thevoltage to power the block instrumentation. The instrumentation blockcan supply power to the sensors included in the detection zone (21) forperforming the measurement, monitor the signal(s) of the sensors andcompare them with reference values. The result(s) of the measurement(s)can be sent to the display system (24).

The electronic circuit (23) may further comprise a data logger to storethe information collected from the sensors within the detection zone(21). Furthermore, the electronic circuit (23) may further comprise acommunication module to send the result(s) of the measurement(s) byradiofrequency, e.g. to an external receiver.

For designing and constructing the electronic circuit (23), preferablywhen it is a microelectronic circuit, can be used suitable knownprinciples known to one skilled in the art, for example, those disclosedin J. Alley Bran, Larry R. Faulkner, “Electrochemical Methods:Fundamentals and Applications”, John Wiley & Sons, 2001, ISBN0-471-04372-9, Jordi Colomer-Farrarons, Pere Lluís Miribel-Català, “ASelf-Powered CMOS Front-End Architecture for SubcutaneousEvent-Detection Devices: Three-Electrodes amperometric biosensorApproach”, Springer Science+Business Media BV, 2011, ISBN978-94-007-0685-9.

The display system (24) may allow the test strip of the presentinvention to show a visual indication of the result of the measurement.This signal can be demonstrated by using a screen, for exampleelectro-chromic, light emitting diode, LCD, etc. Some of these displaysystems are described in CG Granqvist, electrochromic devices, Journalof the European Ceramic Society, Volume 25, Issue 12, 2005, pages2907-2912; Fundamentals of Liquid Crystal Devices, Author (s): Deng-KeYang, Shin-Tson Wu Published Online: 19 OCT 2006, DOI:10.1002/0470032030.

In a particular embodiment, the display of the results may be due to achange of color produced by an electrochemical composite absorbed in aporous matrix (eg, Prussian blue, etc.) comprised in the test strip.

1. A fuel cell comprising: a) at least one microfluidic channel thatallows capillary flow of at least one suitable fluid for generatingelectricity, b) at least one receiving absorbent region coupled to eachmicrofluidic channel, c) at least one collecting absorbent regioncoupled to each microfluidic channel, d) a cathodic zone formed by atleast a cathode coupled to each microfluidic channel, and e) an anodezone formed by at least an anode coupled to each microfluidic channel,where each receiving absorbent region and each collecting absorbentregion are coupled to one of the microfluidic channels such that whenthe fluid suitable for generating electricity is deposited on thereceiving absorbent region, it flows by capillary action through themicrofluidic channel to reach the collecting absorbent region where itis absorbed.
 2. The fuel cell according to claim 1, wherein each of themicrofluidic channels is made of paper.
 3. The fuel cell according toclaim 1, wherein each of the regions receiving and collecting absorbersare made of paper.
 4. The fuel cell according to claim 1, wherein atleast one electrode selected from the group consisting of any one of theanodes and any one of the cathodes coupled to each microfluidic channelcomprise at least one enzyme catalyst.
 5. The fuel cell according toclaim 1, wherein each microfluidic channel has coupled a cathodic zonecomprising at least one cathode and it has a porous structure to receiveand interact with oxygen from the atmosphere.
 6. The fuel cell accordingto claim 1, comprising a single microfluidic channel.
 7. The fuel cellaccording to claim 1, comprising a maximum of three separated receivingabsorbent regions, each coupled to the microfluidic channel that allowsthe capillary flow of at least one suitable fluid for generatingelectricity.
 8. An analysis device comprising: i) at least one fuel cellsuch as described in claim 1, ii) at least one analysis microfluidicchannel that allows the capillary flow of a liquid sample, iii) at leastone receiving absorbent region coupled to each analysis microfluidicchannel, and iv) at least one collecting absorbent region coupled toeach analysis microfluidic channel where each receiving absorbent regionand each collecting absorbent region are connected to an analysismicrofluidic channel so that when a liquid sample is deposited in thereceiving absorbent region, it flows by capillary action through theanalysis microfluidic channel to reach the collecting absorbent regionwhere it is absorbed.
 9. The analysis device according to claim 8,comprising at least one conductive track connecting any one of the fuelcells within the analysis device with at least one element selected fromthe group consisting of at least one electrochemical sensor, at leastone display system to visualize the results of the analysis and at leastone electronic circuit.
 10. The analysis device according to claim 1,comprising at least one electrochemical sensor coupled to each analysismicrofluidic channel and at least one conductive track connecting atleast one of electrochemical sensors with at least one of the fuel cellscomprised in the analysis device.
 11. The analysis device according toclaim 8, comprising at least one display system and at least oneconductive track connecting at least one of the display systems with atleast one of fuel cells comprised in the analysis device.
 12. Theanalysis device according to claim 8, comprising at least one electroniccircuit and at least one conductive track connecting at least one of theelectronic circuits with at least one of the fuel cells comprised in theanalysis device.
 13. The analysis device according to claim 8, furthercomprising: v) at least one electrochemical sensor connected to eachanalysis microfluidic channel, vi) at least one display system tovisualize the results of the analysis, vii) at least one electroniccircuit, and viii) a plurality of conductive tracks connecting each oneof them at least two of the elements included in the analysis device andselected from the group consisting of at least one of the electroniccircuit, at least one of the fuel cells, at least one of theelectrochemical sensors and at least one of the display systems tovisualize the results.
 14. The analysis device according to claim 8,wherein the receiving and collecting absorbent regions coupled to eachof the analysis microfluidic channel are made of paper.
 15. The analysisdevice according to claim 8, wherein the receiving absorbent regionscoupled to each analysis microfluidic channel are comprised,independently, in one of the receiving absorbent regions comprised inone of the fuel cells.
 16. The analysis device according to claim 8,wherein the collecting absorbent regions coupled to each analysismicrofluidic channel are comprised, independently, in one of thecollecting absorbent regions comprised by one of the fuel cells.
 17. Theanalysis device according to claim 8, wherein each analysis microfluidicchannel is made of paper.
 18. The analysis device according to claim 8,wherein each electrochemical sensor comprising carbon electrodes. 19.The analysis device according to claim 8, wherein each electroniccircuit is a silicon-based microelectronic circuit.
 20. The analysisdevice according to claim 8, wherein each system to visualize theresults of the analysis is a screen printed on paper.
 21. The analysisdevice according to claim 8, wherein at least one conductive track ismade of carbon.